I am sorry about your father's medical condition and there other issues you are contending with.
If your father is incapacitated, then you currently have the right to make medical decisions. You do not have any rights over the financial assets, as things now stand.
IF your father is incapacitated and you do not believe he is of sound mind, in the absence of a POA, your only recourse would be to go to the court and be appointed his guardian/conservator. This would allow you to control everything, but you would not be able to change the beneficiary on the account going to the girlfriend. You COULD use money from that account to pay your father's bills, however.
Whether or not you have time to go through the guardianship/conservatorship proceedings, or whether it makes sense to do so is not clear. You may want to consult with an estate planning attorney just to determine what is involved in the process in terms of timing and costs. Also, if your father is not incapacitated, then you will not be able to get the court appointment(s). It is only to protect him during incapacity. If you DO end up going to court, you will certainly want an attorney to assist you.
Your father's negative stance on the POA issue is unfortunate. I believe every adult person should have this form, in order to avoid the need to go to court.
Best wishes to you and your father!
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I am so sorry to hear about your Dad. I too have gone through this.
Since you have his Medical POA, you can make medical decisions. But unfortunately, you do not have any power over the financial matters for your Dad right now.
A question that I have is, has a determination as to your Dad's mental capacity in order to make a POA now been made? If your father is incapacitated, but he knows who you are, and how much money he has, he may be capable to sign a POA. He of course, has to want you to act in that capacity. If not, then you will have to file for a Guardianship or Conservatorship in which the Court appoints someone to handle his financial matters in lieu of a POA. Then you can handle his finances and possibly change beneficairy designations.
Good luck with your Dad.
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